A secondary battery has high applicability depending on the product group and excellent electric characteristics such as high energy density, and thus not only commonly applied to mobile devices, but also electric vehicles (EV), hybrid electric vehicles (HEV) or the like, as an electric power source. Such a secondary battery significantly reduces the use of the fossil fuels and does not generate by-products caused by the use of energy. Therefore, secondary batteries are drawing attention as an eco-friendly alternative energy source with improved energy efficiency.
A secondary battery includes a cathode current collector, an anode current collector, a separator, an active material, a liquid electrolyte, etc., and has a chargeable and dischargeable structure due to the electro-chemical reaction among the components. Meanwhile, since recently a secondary battery is frequently used as an energy storing source and the need of a battery structure having a large capacity is increasing, a secondary battery pack with a multi-module structure having a plurality of the secondary batteries connected to each other in series or in parallel is commonly used.
A secondary battery pack includes secondary battery modules having a plurality of secondary battery cells aggregated therein and a pack case. In addition to this fundamental structure, a secondary battery pack further includes a Battery Management System (BMS) for monitoring and controlling the status of secondary battery cells or secondary battery modules by applying an algorithm for controlling power supply to a load, measuring an electric characteristic value such as current, voltage or the like, controlling charge and discharge, controlling equalization of voltage, estimating State Of Charge (SOC), etc.
Meanwhile, in order to meet various voltage and capacity requirements, a power storage system may be configured by assembling small-capacity power storage unit racks, each having a plurality of secondary battery packs as described above, in series or in parallel.
In order to operate the power storage system, voltage, current, temperature, SOC, or the like of each power storage unit rack should be continuously monitored. For monitoring the status of each power storage unit rack and efficiently controlling the unit rack, correlations of BMSs included in the power storage unit racks are set, so that one of the BMSs included in the power storage unit racks is set to a master BMS and the rest of the BMSs are set to slave BMS. In addition, the master BMS controls the slave BMSs to integrally operate and control the power storage system.
Recently, with smart grids being at the center of interest, the need for a large-capacity power storage system storing unused power is increasing to implement an intelligent power grid. In order to construct such a large-capacity power storage system, a plurality of power storage unit racks is required and the time and cost proportional to the capacity of the system is demanded for installation and management thereof. Therefore, there is a need to develop a technology capable of easily setting a master BMS and a slave BMS in a power storage apparatus such as the power storage unit racks described above.